QTLs detection for growth and initial latex production in rubber (Hevea brasiliensis)

The objective of this study was to analyse the genetic determinism of growth and latex production in rubber tree by a QTL approach. The plant material consisted of 196 progenies derived from the F1 family RRIM600 x PB217. A genetic linkage map was built for this family with 229 SSR markers (microsatellites) and 198 AFLP markers. Phenotyping was carried out over a 6-year period on a field trial of 5 hectares, with around 2400 trees measured individually. A high broad sense heritability was found for latex production, and a major QTL directly associated to production was discovered (Hbg16a131). This QTL explained from 32% to 59% of the genetic variance of the production traits. It was also associated to other traits that were strongly correlated to production such as inorganic phosphorus and dry rubber content (latex diagnostic), as well as plugging index. This finding indicates the existence of one major gene (or a cluster of genes) located on linkage group 16 and involved in the genetic determinism of latex production. A second important QTL associated to the girth of the trunk (growth) was detected (Hbg3a312). Depending on the age of the trees, it explained from 16% to 28% of the genetic variance of the girth. By contrast, no significant QTL was found for sucrose content of the latex, as estimated independently from the production, so suggesting that sucrose genetic determinism might not include any single gene having by itself some important effect. The application of one ethephon stimulation did not evidence any specific QTL. Those results pave the way for Markers-Assisted Selection (MAS) as applied to clonal selection in rubber. Genotyping the candidates to selection for the 2 QTLs with important effects should allow a much more accurate estimation of genetic values as soon as at the first selection stage. (Résumé d'auteur)